Light microscopy of a swarm of Euglena protozoa in pond water. Euglena is a single_celled plant_like protist with an oozing, ever_changing shape. Its bright green color comes from chloroplasts used in photosynthesis, as in plants. It propels itself with a single, hairlike flagellum located at its leading end. It is attracted to light, which it detects using its red eyespot located near the base of its flagellum. These specimens measure approximately 50 micrometres in length. Their movement has been slowed down due to evaporation of water on the microscope slide. Recorded under Nomarski differential interference contrasts illumination.